Flying forms of the sort for which the extension leg assembly of the present invention is particularly useful are known, for example, from Canadian Patent No. 941,138 in the name of Peter J. Avery, issued Feb. 5, 1974 and granted to the assignee of the present application. In that patent, there is taught a concrete forming structure which comprises -- in the usual form -- a pair of trusses with a plurality of substantially parallel beams placed across the trusses, and a deck formed of a number of panels secured to the beams. The whole structure is bolted together, and is adapted so as to be flown from one position to another by being lifted by a suitable crane or other means. However, when such structures are placed for use in concrete forming, where the concrete floor or slab to be poured is placed on the upper surface of the deck, some adjustment must be provided both to assure that the upper surface of the deck is exactly at the correct height at all places, and also so as to be able to lower the deck away from the underside of the poured concrete slab after it has cured in order that the concrete forming structure may be removed and flown to its next working position.
In the previous patent, noted above, a screw jack was supplied and adapted to be fitted to the bottom chord of each truss at a place beneath a truss upright. Such arrangement was, of course, necessary so as to assure that loads transferred downwardly through the truss uprights and the truss diagonals to the bottom chord would be transferred directly to the supporting surface on which the trusses were standing.
However, in many cases it has been noted that it is desirable to have a wider adjustment of the height of the truss from its working height to its flying height. This may be, for example, particularly so as to accommodate greater than normal floor-to-ceiling heights as may be found in parking garages, commercial and office buildings, the lower floors of hotels where lobbies or convention floors might be accommodated, etc. Also, in some cases a spandrel beam is poured at the same time as a concrete slab or floor, so that it is necessary to reduce the height of the form by more than the usual amount in order to have it clear through the reduced height opening. In any event, it is sometimes necessary to provide an adjustment for the height of the truss of a concrete forming structure having a magnitude of adjustment with a factor of approximately two -- i.e., where the working height may be as much as two times the flying height of the truss.
In not all cases, however, it is necessary or desirable -- because of the additional expense -- to have an extension leg in a truss; but when it is desired to have extension legs fitted to a truss, the substitution of the strandard truss uprights by the extension leg should be easily and quickly made, without the necessity for any additional drilling or rigging, especially in the field. Thus, when it is desired that extension legs be fitted to a truss for a flying form for use in horizontal or substantially horizontal concrete forming, so as to preclude the use of tables, movable dollies and the like, it is desirable to merely replace one part of the truss for each extension leg. By the same token, it is desirable that the extension leg be already fitted or adapted to be fitted with a screw jack assembly at its bottom end, in order that fine adjustment of the final height of the deck can be arranged in the usual manner.
One of the great advantages of using flying forms for concrete forming of the sort taught in the above-mentioned patent, is that such forms are generally made of extruded aluminum. Thus, very much larger forms with larger deck surfaces on which concrete can be poured are possible with aluminum concrete forming structures of the sort referred to than would be possible with steel or wooden structures. It follows, therefore, that it is desirable that the extension legs for such concrete forming structures should also be preferably formed of extruded aluminum rather than of structural steel tubing, I-beams, etc., in order that the amount of increased weight which is added to the concrete forming structure by the addition of extension legs be kept to a minimum.
It is also desirable that other attachments might be easily and quickly secured to the concrete forming structure by attaching them to bolt slots formed in the extension leg. Such additional attachment might be underslung beam forms or connection beams, outriggers, knee braces, etc. In any event, the provision of at least one bolt slot -- and in the preferred embodiment, two bolt slots -- on the outer face of the extension leg assembly can accommodate such attachments.
It has been noted that it is desirable to provide means whereby a screw jack assembly may be secured to the bottom end of the inner leg -- which is the lower leg -- of the extension leg assembly in such a manner that the screw jack assembly may be locked in a down position when it is supporting the concrete forming structure, or in a swung-up position for flying. Lock means are therefore provided on an extension leg assembly according to this invention whereby both positions of the screw jack assembly can be assured. The locking arrangement for the screw jack assembly when it is in its flying position is such that the center of gravity of the screw jack assembly assures engagement of the hooks which comprise the lock, as discussed in greater detail hereafter.
In general terms, the extension leg for concrete forming structures, provided by this invention, consists of a first, outer leg which has a back and a front surface, and which is secured to the top and bottom chords of the truss; and a second, inner leg also having front and back surfaces which is telescopically engaged within the first leg. Of course, an interior opening is formed axially within the first leg so as to accommodate the second leg, and the second leg is so shaped at its back surface as to accommodate those portions of the bolts which secure the upper leg to the top and bottom chords of the truss which are on the inside of the back face of the upper leg. pairs of holes are formed through the front and back surfaces of the inner leg, having predetermined spacing between them -- in general, a plurality of holes where the same predetermined spacing exists between any adjacent pair thereof; and at least two holes are formed through the front and back surfaces of the outer leg so that a pair of pins can be inserted, one through each of the holes, to secure the legs against relative axial movement one to the other. (It should be noted that, for purposes of load bearing, a pair of pins is usually inserted through each of the legs when they are locked in position.)